Many manufacturing applications require the generation of a linear force for moving of machine equipment. Conventional AC and DC motors produce a rotary torque about an axis which must be converted into a linear force before it can be used in such applications. Such conversion is accomplished by a screw and nut, a sheave and cable, or a rack and pinion, among other designs. These designs are problematic in that they tend to wear out relatively quickly, and they are incapable of producing high linear speeds.
Linear motors are also known which directly product a linear force in response to an electric input. Typically, a linear motor takes advantage of the variable magnetic reluctance produced in the vicinity of slots in a pole face of a magnetic member. An armature of a magnetic material, having windings therein, is urged to step from position to position along the pole face as defined by the slots or, alternatively, the magnetic member is movable while the armature is stationary.
In such designs, the armature portion usually comprises a coil disposed within a lamination stack and surrounded by an epoxy block. A cooling tube is typically provided adjacent the epoxy block for drawing heat from the armature.
The force which such linear motors are capable of producing is limited by resistive heating in the windings of the armature of the motor. The normally used copper cooling tube requires mechanical retention within the epoxy case, and provides somewhat limited armature cooling capacity because the epoxy itself acts as an insulator for the coil assembly. By reducing heat dissipation, performance of the linear motor is adversely affected, and the forward thrust capability declines.
Accordingly, it is desirable to provide an improved armature design with increased cooling capacity.
My U.S. Pat. No. 5,751,077, which is hereby incorporated by reference in its entirety, provides an improvement over the above-referenced linear motors by providing a linear motor with an armature which is fully enclosed within a sealed metal case, and an electrically nonconductive fluid is circulated within the case in direct contact with the lamination stack for cooling the lamination stack and coil assembly. The metal case is sealed by means of a thin cover which is positioned directly adjacent the magnetic plate. The spacing between the magnet plate and the sealed metal case is critical and preferably maintained at approximately less than 0.040 inch to maintain high forces.
A problem with this design is that when cooling fluid is forced through the sealed metal case, the pressure of the fluid tends to bubble up the thin cover, which may cause the cover to actually contact the magnet plate, which will adversely affect operation because the rubbing of the cover against the magnet plate can cause damage, such as chipping and scraping, and the resulting metal chips or shavings may cause further operational problems.